When a thin film is formed on a substrate, for example, a semiconductor wafer (hereinafter, referred to as a “wafer”), conventionally, a rotary table is provided in a processing container to be rotatable around a vertical axis, a plurality of wafers are placed on the rotary table, and a film formation processing is performed while rotating the rotary table. For example, in a case of atomic layer deposition (ALD), a plurality of gases, each reacting with the surfaces of the plurality of wafers, are supplied in sequence, so that a plurality of layers of reaction products are laminated, thereby forming a thin film. According to the method, since the film formation can be performed on a plurality of wafers at the same time, the production efficiency is good, as compared with a single wafer method. Furthermore, since the film formation is performed on respective wafers while rotating the rotary table, a uniform film formation processing is enabled for respective wafers.
However, the present inventors have found that profiles between respective wafers are certainly uniform, but there is still a problem about the in-plane film thickness uniformity of the wafers. This will be described with reference to FIGS. 8 and 9. For example, in a case where five wafers 102 are placed at regular intervals in the circumferential direction on a rotary table 101 that rotates around an axis P as a rotation center, it has been confirmed that, for example, even though radical components for film formation are supplied uniformly on the rotary table 101, the film thickness tens to increase in both end portions in the radial direction connecting the rotation center of the rotary table 101 and the center of the wafer 102, as compared with the center of the wafer 102.
As illustrated in FIG. 9, in a case of a bare wafer, there is not much difference in film thickness between the center of the bare wafer and both end portions in the radial direction. However, in a case of a patterned wafer, the film thickness in both end portions in the radial direction is larger than that in the center of the wafer. Further, in FIG. 9, the term “Center”, as illustrated therein, refers to a central end portion of the rotary table 101 in the radial direction connecting a wafer center PW and the axis P serving as the rotation center of the rotary table 101, and the term “Edge” refers to an outer end portion of the wafer in the radial direction.
The reason is that, when a processing is performed while rotating the rotary table 101 as illustrated in FIG. 8, the amount of the radical components consumed is generally increased in the center of each wafer 102, as compared with both end portions in the radial direction, so that the center eventually becomes thinner, and the adhesion amount per hour of the radical components per area is decreased in the center. And, it is not a serious problem in the case of the bare wafer. However, in the case of the patterned wafer, since a minute unevenness based on the pattern is formed on the surface of the wafer, the reaction area is ten times wider than the case of the bare wafer, so that the difference in consumption amount becomes remarkable.
In this regard, when the film formation processing is performed on a plurality of wafers on the rotary table at the same time, as a technique for improving the uniformity of the film thickness in each wafer, it has been suggested to arrange an annular temperature control unit in a periphery of the wafer (see Japanese Patent Laid-Open Publication No. 07-249580).